With the overall requirements of terminal application products for stronger integrated functions, higher resolution, faster response speed and larger storage capacity, the development tendency of the flexible printed circuits (FPCs) is becoming more obvious in high frequency, high speed and functionalization. For example, mobile phones have integrated more and more functions, including camera, Bluetooth, Wi-Fi, 3G internet access, etc. besides the conventional voice and video functions; in the future, fingerprint identification and all kinds of sensor components will be integrated too, making the broadband further increased and facilitating constant development of high-frequency and high-speed application technologies. High Dk decreases the signal transmission rate and high Df makes signals partially transformed into heat energy and lost in baseplate materials; therefore, decreasing the Dk/Df has become a hotspot in the baseplate industry and all kinds of new technologies and baseplate products with regard to Dk/Df have emerged in large numbers.
Currently, the material most commonly used in FPCs to solve the problem of high-frequency signal transmission is liquid crystalline polymer (LCP), for its characteristics of low dielectric constant and low dielectric loss required in high-frequency transmission. Take iPhone, the leading brand of smart phone for example, after it is disassembled, two FPCs are found using LCP as the cable for high speed transmission of signals. The imported mobile communication of high-frequency transmission is gradually emerging in the field of smartphone.
Although LCP FPC has inborn advantages in high frequency characteristics, the high-temperature equipment and conditions for processing are obviously different from the current mainstream process technology of low-temperature quick press for FPC. Therefore, apart from the processing equipment replaced by a pressure-transmitting device for pressing LCP base material in high temperature, the production rate is also affected. To address the application problem, high-frequency adhesives for low-temperature (<180° C.) adhesion are becoming an important option in the development of FPC materials.